Based on recent progress in techniques for silver halide photographic materials used as general negative film for camera use (hereinafter, also denoted simply as photographic materials or negative film), photographic materials having a higher speed than the common speed of ISO 100 have become commercially available, one after another. Furthermore, the use of zoom lenses of a long focal length has increased along with popularization of compact cameras for amateur photographers. Thus, the full open value (lightness) of a lens has become smaller and the percentage of under-exposed scenes has increased compared to the past, resulting in lowering print productivity and finished print quality in photofinishing laboratories, and consequently, an immediate solution thereof is therefore desired.
When printing from an under-exposed negative film, high-light and shadow portions of the main subject in the under-exposed scene show poor density representation (tone reproduction), so that when the density of the subject is increased, the overall density increases, resulting in an excessively dark print; on the contrary, when the overall density is decreased, the density of the subject becomes lighter, resulting in blurred images and leading to print images not acceptable to customers. In such situations, the acceptable range of proper print density becomes narrower, resulting in printing difficulty.
Such appearance of under-exposed scenes often occur not only in the case of indoor photography, night photography, scenes having a relatively high dark proportion and photographing by using darker lenses such as a zoom lens, but also in the case of so-called photographing against light, such as a dark subject against the light background of the sky. It was proved from a survey that in such photography against light, few photographers realized that dark scenes were really photographed, often resulting in cases that the photographers discovered under-exposed photography when they obtained their prints from under-exposures. It was further proved that the difference between realization or expectation of the photographer and the real finished print quality was wide, often producing dominant causes of complaints for poor quality.
The speed in the foregoing photography system is generally called effective speed. It is commonly known that the effective speed in the negative-positive system using color negative film and color paper is more or less related with but is not simply connected to the commonly used color negative film speed as defined in ISO standards (hereinafter, also denoted simply as ISO speed).
Means for solving print quality problems of under-exposed scenes include, for example, enhancement of the ISP speed of color negative film. The silver halide emulsion speed is mainly dependent on silver halide crystal size and a technique of using a large grain silver halide emulsion to achieve enhanced speed, which is readily feasible and commonly practiced, as is known in the prior art or reported in literatures.
In fact, enhanced ISO speed can be achieved by the use of such a large silver halide grain emulsion, thereby also enhancing the effective speed in printing to some extent; however, the effect of solving the foregoing problems is low and on the contrary, the use of large silver halide grains produces rough graininess of the subsequent printed image. Specifically in cases when printed at a large magnification such as a 2L size or panorama size, printed images become coarse, producing complaints of prints being unacceptable by the photographers.
A single channel printer built-in with a scanner (hereinafter, also denoted as “1 ch. printer”) can faithfully scan negative images using a CCD camera (i.e., image scanning) and can also conduct appropriate exposure control taking account of pattern analysis of the respective scenes. However, the fact remains that the print yield cannot be enhanced enough even by use of such printers and finished print quality by no means reaches satisfactory levels.
As described above, the print yield can be enhanced to some extent by recent progress in printer technique but further improvements are desired.
As a result of analysis by the inventors of this application using various types of printers and photographic materials to explore causes for the foregoing problems, it was proved that variation in color reproduction, specifically in under-exposures greatly affect variation in finished print quality (which is also called print level variation) and secondly, variation in color reproduction at a normal exposure level was also explored. It was further proved from a survey of print quality on the market that users complained that image quality of under-exposures did not meet the given quality standard for the respective film speeds.
To improve the print level variation of under-exposures, an attempt of stabilizing the density balance along with exposure variation over the range of the under-exposed region to the over-exposed region have been made through enhancement of photographic material speed by applying techniques proposed or disclosed in photographic literature and patents, but marked effects have not been achieved by anyone thereof. The correct printing exposure condition set in the printer is set by attaching importance to an average value on the market for each of various film speeds. Consequently, in response to variation of color temperature in the respective scenes (for example, according to a photographing environment such as fine weather, cloudy weather, shade and electric flash light), exposure conditions for a specified film speed, e.g., ISO 800 often results in a calculated value corresponding to a film speed of ISO 200 to 400, so that delicate exposure control is not achieved.
Appearance of under-exposed scenes accounts for approximately 20% in the current negative-positive system. However, total image quality of the thus under-exposed scenes is markedly inferior to normal- or over-exposure scenes accounting for 80% and therefore, enhancement in image quality of the under-exposed scenes is desired together with enhancement in total print image quality and print yield. As described in literature, for example, “Shashin-Kogaku no Kiso Ginene-Shashin” (Fundamentals of Photographic Engineering of Silver Salt Photography), published by Corona Publishing Co., it is known that sharpness and graininess greatly affect total image quality. For example, JP-A No. 10-268467 (hereinafter, the term, JP-A refers to Japanese Patent Application Publication) discloses a method of enhancing image quality by RMS granularity at a normal exposure or in vicinity thereof. However, total image quality in under-exposed scene, which differs from that of normal-exposure scenes cannot be accounted for only in terms of sharpness and graininess. Using a large amount of silver coverage or a dye forming coupler for enhancement of image quality results in an increase in cost, therefore, it cannot be said to be an efficient method.
Recently, besides the above-described printers of a conventional exposure control system, digital type or hybrid type printers are on the rise, in which image density information is obtained as digital information by scanning developed negative images and after being subjected to image processing, printing is performed based on that information.
In cases when using such printers, in addition to the foregoing problems in exposure control at under-exposure, problems arose with compression or deficiency of information when digitizing (or quantizing) information. This is due to the fact that negative film usually has information of a density of up to 3.5 (or gradation number of more than 300 levels) and contrary to that, an image in the standard format has to be compressed to a 256 level gradation at the time of quantization and a part of the information is often not properly transformed.
However, one disadvantage thereof is that when an under-exposed, low contrast scene is converted to proper contrast, incompatibility of the density range of the negative film (hereinafter, also denoted as negative density range) and the range of quantization excessively enhances contrast to a level higher than necessary for most people, resulting in deteriorated graininess or producing problems in that an excessive decrease of contrast is caused in high contrast scenes having a main subject differing in luminance from the background. Consequently, it was proved that the dynamic range was not fully employed, often producing an unnatural image print and tending to cause print level variation. In this regard, an improvement was made using a complicated algorithm with respect to some of phenomena, but it lowered productivity per hour and proved to be unacceptable in practice.
It was further proved that rapid access and diversification of photographic processing, according to recent market trend in the photographic industry, caused lowering in the SN ratio at the stage of digitization in silver halide photographic materials using silver above a given amount. This is assumed to be due to insufficient desilvering, in which metallic silver is retained in the coat due to an exhausted bleaching solution, resulting in lowering in SN ratio at the stage of negative-positive conversion of negative images in the process of digital printing. In cases when metallic silver was retained in processed negative film, location for the respective pictures was not accurately set up at the stage of scanning the negative film in a printer. Specifically in a scene taken with a low-priced camera which was poor in film-transport accuracy, even data of portions not relevant to the real scene (minimum density portions) were read in image processing, so that the dynamic range of positive image data (8 to 16 bits) was not effectively employed to perform positive image processing, resulting in a print exhibiting contrast, which was incongruity with a print obtained by a conventional analog type printer.